At least in imperative code the "how" is explicit. In functional code it's implicit and you need intimate knowledge about compiler and/or runtime to know what's going to happen.
But also, writing imperative code doesn't guarantee explicit performance characteristics. Whether you mutate references or not, you still need to know which operations are fast and which are slow.
In JavaScript, concatenation, [...array1, ...array2], is non-mutating and slow. Adding an element to the end, array.push(x), is mutating and fast. But adding an element to the beginning, array.unshift(x), is mutating and slow. So even if you're sticking to mutation, you still need to know that push is fast and unshift is slow.
And yeah, sorry, "in JavaScript" is not quite right. I meant in my browser. This is not part of the spec, and it's not mentioned in the documentation. Is it the same in other browsers? Who knows. To me, this is just as much "you need intimate knowledge about compiler and/or runtime to know what's going to happen".
This year it's slow. I wouldn't count on that being true in five years. I mean, it might, it might not. There's a risk in optimizing too much for current conditions. You can easily end up over-fitting for the current set of coincidences, and end up with less readable code that's actually slower in the long run.
But by all means, measure and improve until it's fast enough.
Unless there is clear evidences upfront that the project will be a piece of software where local performance is highly critical, it makes sense to favor code readability and maintainability over optimality.
Of course, you can have different level of code quality whatever the paradigm retained. Most languages out there will allow you to mix different paradigms anyway.
Given this fact, we would surely better served with an article like "When to favor expression in each paradigm available in your favorite language".
In my experience, software engineers "think" imperatively. First do this, then do that. That's what we do in everyday life (open a random cooking book..) and that's also what the CPU does, modulo some out-of-order and pipelining tricks. A declarative style adds some extra cognitive load upfront. With training you may get oblivious to that, but in the end of the day, the machine does one thing after the other, and the software engineer wants to make it do that. So, either you express that more "directly" in an imperative style, or try to come up with a declarative style which may or may not be more elegant, but that this ends up more readable or maintainable is on the functional proponents to prove.
It’s funny you mention recipes, because i’ve always been frustrated by traditional recipe descriptions that muddle concurrency and make it difficult to conceptualize the whole process. E.g. the table structure here is superior to step by step http://www.cookingforengineers.com/recipe/158/Dark-Chocolate...
Tbf, I agree with the recipe criticism. Would be neat with a dependency graph instead of a step-by-step list of things to do when baking a cake. Would have saved me a lot of headache in the past. (The table in your link expresses a tree, which is probably sufficient for most purposes.)
I hear this often. In the past the claim used to be that they "think" object-oriented. This is a thinly veiled argumentum ad naturam.
> ... on the functional proponents to prove
Prove your own claims before you demand proofs from other people. And by prove I mean really rigorous thinking, not just superficially seeking confirmation for the things you already believe either way.
B: Prove it!
A: No, you prove first! With really rigorous thinking, please!
People are doing A. Someone says "Do B instead!". "Why should we do B?" "Well, why should you do A?" At the end of that extremely unproductive exchange, what are people going to do, A or B? They're going to keep doing A, because they were already doing that, and nobody gave them any actual reason to change.
So "burden of proof" isn't meant in the sense of this being a formal debate, with rules. It means that, when ahf8Aithaex7Nai said "Prove your own claims before you demand proofs from other people", that ahf8Aithaex7Nai is wrong. OOP is the current default in terms of the bulk of professional programming; if FP advocates want that to change, it's on the FP advocates to provide reasons, not on the OOP advocates to prove the correctness of the status quo.
The proponents of status quo only need to prove that the existing approach works and is useful. And I think that is proven already by the very existence of status quo. It wouldn't be there if it wasn't somehow useful.
It is terrible on a system level with concurrent execution, there you really need all the safe guards.
Sure, but let's also not confuse "optimal" with "reasonable". One of the major challenge of modern programs is how slow they are at every level. Very often, this bad performance can be attributed to a style of programming that tries to completely ignore that the program will run on a real machine with real hardware. A little bit of mechanical sympathy (e.g., operations that make good use of the CPU caches or don't confuse the branch predictor) can yield a program that is 10x faster than a naive implementation, with little to no loss of readability or maintainability. (In fact, as noted by Nelson Elhage [1], faster programs enable simpler architectures, which helps make them more readable and maintainable.)
In FP languages, programmers face an extra difficulty: the distance between the code they write and the machine code that will be executed is greater than in languages like Rust or Go. They will need to be knowledgeable about the language, its libraries, and its compiler to avoid the pitfalls that could make their programs slower than would be reasonable (e.g., avoiding unnecessary thunking in Haskell).
[1] https://blog.nelhage.com/post/reflections-on-performance/#pe...
First of all, one of those languages is not like the other (Go is closer to JS than to Rust) - second, we really can’t reasonably guess at the produced assembly, even C compilers do some insane transformations leaving the code nothing alike the original, let alone more expressive languages.